1. Field of the Invention
The present invention relates to photography in general, and more particularly to a mechanism for adjusting a camera function such as focus or exposure.
2. Description of the Prior Art
It is known in early cameras of the type having a folding bellows, which connects the camera body and a variable focus objective lens, to provide a rack and pinion mechanism for moving the camera lens back and forth along its optical axis for focus adjustment. Examples of such cameras are disclosed in U.S. Pat. No. 800,081, granted Sept. 19, 1905 in the name of Davis and U.S. Pat. No. 3,092,001, granted June 4, 1963 in the name of Schlapp. Generally, these cameras include a manually rotatably thumb wheel which is connected by means of a rotation shaft to the pinion for moving the pinion along the rack to adjust the focus of the objective lens. While these early cameras were satisfactory for their time, the rack and pinion as well as the thumb wheel are typically located outside of the main camera housing and therefore are not sealed against contamination by dirt or other foreign matter.
Later generation cameras, in particular the pocket-type cameras for size 110 film, are provided with a manually operable focus or exposure slider whose upper half or manipulatable portion projects through a slot in the camera body. The manipulatable portion of the slider may include an indicator pointer which is aligned with focusing or exposure scale indicia, such as distance setting numbers or ambient light indicating symbols, located on an exterior face of the camera body. When, for example, focusing adjustment is desired, the manipulatable portion of the slider is manually pushed along the camera slot causing the camera lens to be moved along its optical axis. While the slider provides a convenient adjustment means for focusing or exposure control, it is possible for an operator to appreciably increase the frictional force which oppose movement of the slider by pressing down sufficient hard on the slider to cause the slider to rub against is supporting or guide surface. Such frictional forces will, of course, prevent a smooth or easy action of the slider, possibly resulting in imprecise focus or exposure settings and wear of parts.